JP-2007-85332A shows a fuel supply system which is provided with a feed pump and a high-pressure pump. The feed pump pumps up fuel in a fuel tank and supplies the fuel to the high-pressure pump. The high-pressure pump pressurizes the fuel and supplies the pressurized fuel to an internal combustion engine. The high-pressure pump is comprised of a cam driven by a camshaft, a plunger reciprocated by the cam, a fuel pressurizing chamber of which inner pressure is varied by the plunger, and a cam chamber accommodating the cam shaft and the cam. The fuel discharged from the feed pump is introduced to the fuel pressurizing chamber through a first pipe. A second pipe is branched from the first pipe to introduce the fuel to the cam chamber. A part of the fuel discharged from the feed pump flows into the second pipe through the first pipe. The fuel supplied from the feed pump to a housing through the second pipe functions as lubricant lubricating sliding portions of the high-pressure pump.
As described above, the second pipe is branched from the first pipe. Since these pipes are made by aluminum die-casting, it is likely that a metallic burr is produced at a portion where the second pipe is branched. The burr may fall off inside of the pipes due to fuel flowing pressure and may mix in the fuel flowing through the pipes. A cleanliness of the fuel which is to be supplied to the cam chamber may be deteriorated.
Besides, since the first pipe introduces the fuel into the fuel pressurizing chamber of the engine, it is necessary to provide an orifice in the second pipe in order to ensure fuel quantity supplied to the engine through the first pipe and to restrict an excessive fuel supply to the cam chamber. Foreign matters contained in the fuel easily adhere on the orifice. The foreign matters may fall off inside of the second pipe and may mix in the fuel flowing through the second pipe. The cleanliness of the fuel which is to be supplied to the cam chamber may be deteriorated.
Furthermore, the foreign matters may adhere on a fuel quantity regulation valve provided in the first pipe. The foreign matters may fall off inside of the first pipe and may mix in the fuel flowing through the first pipe. Then, the foreign matters flow from the first pipe to the second pipe by pulsation of the feed pump, whereby the cleanliness of the fuel which is to be supplied to the cam chamber may be deteriorated.
As described above, in the system having the second pipe branched from the first pipe, the burr of the pipes and foreign matters adhering on the orifice and the fuel quantity regulation valve may deteriorate the cleanliness of the fuel which is to be supplied to the cam chamber, so that the lubricating ability of the fuel may be deteriorated. An anti-seizure of the sliding portion of the high-pressure pump may be deteriorated.